what is your rpm w/3.73 and 315's/6sp

[Diesel Dan]

Hello friends,



I can't figure out what happened. I put on 315's and figured that my speedpo was off apx 6 mph at 70. (actual speed is apx 76 when showing 70 on the speedo. This was at 2000 rpm. Had the computer reprogrammed for the 315's by a dodge mechanic/ obdII scanner. Now at 2000 rpm's i am showing 68 mph!!! it should have gone up 5-6 mph instead it went down 2 mph. This is baffeling.



Any comments out there



Please post what your speed is at 2000 rpm if you have 315's and 373's and a 6 speed for comparison



and if you noticed a change w/ reprogramming for 315's



Thanks



DD

 

[Udaloy]

I thought the computer could only be reprogrammed for up to a certain size tire, with 315's being well beyond the limit. I have 315's on my '02, and at highway speeds, it's 10 mph off. I installed a SuperLift Tru-Speed recalibration box, and everything is fine.

 

[klenger]

Try plugging your numbers into the calculator at the following link:



http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls

 

[DougR]

The guy obviously messed up on the programing. It should read 76 @ 2000 rpm as you stated. That sounds about right. My Ford diesel ran those same numbers exactly. My new DC has 4. 10 gears and runs 70 @ 2000 rpm. All with 315's,although I have an Auto.

 

[DougR]

BTW,315's are almost exactly a 10% increase in gearing,as well as your speedo and odometer. I checked mine today and 70 mph on the speedo was 76. 9 on the gps.

 

[klenger]

I plugged 315 tire size into the calculator I mentioned above and got the following. I am assuming that the 315 tires are 70 series profile.

 

[Greg Boardman-RIP]

Dan,

Maybe you told him the wrong number for the tires rpm? I'll bring my GPS to the dyno day and we'll check your numbers.

 

[Diesel Dan]

Hi guys



Udaloy,

w/ 03's you can imput the revs per mile of any tire into the computer. According to BFG's web site the 315/70/17 is 601 revs per mile.



DougR



The guy does this for a living so i trust his work completely. This is why i am stumped



Klenger



Thanks for the chart. It confirms what i thought it should be. I will print it and take it to the dyno days in a few weeks.



Greg

Thanks buddy. I hope the guy w/ the OBDII scanner will be there so we can get it right



Thanks to all



DD

 

[Diesel Dan]

TTT